In a message dated 4/21/00 8:34:47 AM Eastern Daylight Time,
TEDSDAKOTA@aol.com writes:
> If it drops the vacuum, ya could be in trouble. This will cause the PCM to
> > see a higher MAP sensor voltage ( as in "engine under load") and it
> > will feed more fuel..
>
> I have less vacuum with the M1..My trucks running rich..Could this be
the
> problem ??
> Thanks, Ted O.
Yep, the correct valu resitor or (better yet) potentiometer would prolly help.
Lemme dig up some idle fuel tablenumbers to make a point... ..
Hokay, (sorry it's GM) These are closed throttle / base fuel table
values use in fuel calcs in a MAP system..
The "V" pointer is where a typical idle vac was before a mild cam
installation.
Notice the higher the vaccuum, the lower the fuel requirement..
|
RPM HI<< --V-----------------VAC ----------------------->LOW
600 | 28.1 29.4 32.7 34.4 43.8 46.9 34.4 43.8 36.7
800 | 34.4 29.4 30.8 37.5 43.8 43.8 43.8 43.8 43.8
1000 | 34.1 30.2 30.8 37.5 43.8 43.8 43.8 43.8 43.8
After the new cam:
Notice how the base pulse value gets higher as the vaccum goes down.
This is to accomidate engine load.. If vacuum drops the PCM thinks
the load ha increased and is programmed to provide more fuel.
The pointer is in the 3rd collumn now..
RPM HI<< -------------V--------VAC ----------------------->LOW
600 | 28.1 29.4 32.7 34.4 43.8 46.9 34.4 43.8 36.7
800 | 34.4 29.4 30.8 37.5 43.8 43.8 43.8 43.8 43.8
1000 | 34.1 30.2 30.8 37.5 43.8 43.8 43.8 43.8 43.8
To aggrivate the situation even further, the timing is probably being
advanced as the vacuum drops too.. Again, to help overcome a
percieved load on the engine. Sorry about the sucky diagrams.
I hope it makes some sense.
Mike V
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